1. Field of the Invention
The present invention relates to an installation structure of a sensor and a projector apparatus having the same, and particularly to an installation structure of a sensor for detecting an airflow rate and an air velocity by sensing the flow of the air suctioned due to the differential pressure, and a projector apparatus to which the installation structure of the sensor is applied.
2. Description of the Background Art
In the projector apparatus, the light emitted from a light source is guided by an optical system to produce an image which is then enlarged and projected onto the screen located toward the front thereof. An example of this projector apparatus will be hereinafter described. As shown in FIG. 7, a projector apparatus 101 has a casing 102 which includes therein an optical system unit 105 for generating an image, a first lamp unit 107 and a second lamp unit 108 each serving as a light source, a control circuit board unit 106 for controlling a series of operations of optical system unit 105, and the like. One of first lamp unit 107 and second lamp unit 108 serves as a spare lamp unit.
During the operation of projector apparatus 101, optical system unit 105 and control circuit board unit 106 generate heat. Furthermore, when the lamp attached to each of first (second) lamp units 107, 108 emits light, first (second) lamp units 107, 108 also generate heat. The heat emitted from optical system unit 105 and first (second) lamp units 107, 108 causes an increase in temperature within casing 102, which may affect the operation of control circuit board unit 106. In addition, the lifetime of each lamp attached to first (second) lamp units 107, 108 may be shortened.
In order to alleviate the above-described defects, a cooling mechanism for cooling the inside of casing 102 is provided in projector apparatus 101. In other words, a first fan 109 and a second fan 110 for introducing the outside air (air) into casing 102 to air-cool the inside of casing 102, and a third fan 111 for introducing the air into first (second) lamp units 107, 108 are disposed within casing 102.
As first fan 109 and second fan 110 are rotated in such a manner that the pressure inside casing 102 is rendered negative relative to the pressure outside casing 102, the outside air (air) is introduced from an inlet port 103 disposed on the side of casing 102 through a filter 114 into casing 102. The air introduced into casing 102 flows through a duct 104 (an arrow 131) to cool optical system unit 105 and control circuit board unit 106.
The air used to cool optical system unit 105 and the like then cools first lamp unit 107 and second lamp unit 108 disposed behind optical system unit 105 and the like, and is subsequently discharged through the rear face of casing 102 to outside thereof. Thus, the inside of casing 102 is air-cooled.
In this series of air-cooling operations, the amount of the air introduced into casing 102 is sensed by an airflow rate sensor 121. As shown in FIG. 8, airflow rate sensor 121 is installed in a predetermined position on the outer surface of duct 104.
As shown in FIG. 9, airflow rate sensor 121 is provided with a through hole 122, within which a detection unit 123 such as a heater is disposed. Duct 104 is provided with an opening 125 having a relatively small diameter (approximately 1 mm), so as to allow adjustment of the inflow rate of the air into airflow rate sensor 121.
When the air flows through duct 104, the pressure inside duct 104 is rendered negative relative to the atmospheric pressure outside duct 104, which causes the air to flow from outside duct 104 via through hole 122 of sensor 121 and opening 125 toward the inside of duct 104. The airflow rate may be calculated based on the output voltage resulting from the temperature difference and the like caused in detection unit 123 by the air flowing through the through hole 122 of airflow rate sensor 121. It is to be noted that Japanese Patent Laying-Open No. 2007-304481 discloses a projector apparatus provided with a cooling mechanism.
The cooling mechanism of the conventional projector apparatus, however, poses the following problems. In order to prevent foreign substances such as dust contained in the air from affecting the optical system unit, filter 114 is disposed in inlet port 103 of duct 104 (see FIG. 7). As shown in FIG. 10, in the state where filter 114 is not clogged at first, a predetermined amount of air (arrow 131) is introduced through filter 114 into casing 102.
Then, a differential pressure (P1−P2) resulting from the flow of the predetermined amount of air is produced between the spaces outside and inside duct 104, which causes the air to flow (an arrow 141) from outside duct 104 via through hole 122 of airflow rate sensor 121 and opening 125 toward the inside of duct 104 (steady state).
Then, as shown in FIG. 11, when filter 114 catches foreign substances and starts getting clogged, the amount of the air taken in through filter 114 gradually decreases (an arrow 132). Accordingly, the pressure inside duct 104 falls below the pressure in the steady state, resulting in an increase in differential pressure (P1−P2) between the spaces inside and outside duct 104. This causes the air to flow through the through hole 122 of airflow rate sensor 121 at a higher velocity (an arrow 142).
However, the diameter of opening 125 in communication with through hole 122 is configured to be smaller than that of through hole 122. Therefore, an increase in flow velocity of the air may prevent the air from smoothly flowing through opening 125. Thus, turbulence tends to occur in the flow of the air (an arrow 143) inside through hole 122 located in front (upstream) of opening 125. This results in variations in the flow rate sensed by detection unit 123 of airflow rate sensor 121, which may prevent sufficient cooling of the inside of casing 102.